1. Field of the Invention
This invention relates generally to brake systems for heavy duty vehicles, and particularly relates to improvements in pneumatic braking systems having multiple control systems.
2. Description of the Background Art
Pneumatic or air pressure-actuated brake systems for large vehicles are well known. Such brake systems utilize pressurized air to actuate a brake assembly in a brake chamber of the vehicle. Air actuation of the brake assembly is known in the art as a service brake application and is carried out to slow down or stop the vehicle while it is in motion. In addition to service brakes, it is common for heavy duty vehicles to include spring brakes, which are activated in a parking brake application to lock the brake assemblies in a park position when the vehicle is at rest. The brake assembly is locked in the park position through the expansion force of a spring located within the brake chamber, which is kept compressed in the non-activated state through application of air pressure against a diaphragm. Actuation of the spring brakes is effected by venting or exhausting the pressurized air in the lines coupled to the diaphragm, and the spring brakes are deactivated by reintroducing pressurized air into the lines. Such known systems are disclosed, for example, in U.S. Pat. Nos. 5,190,357, 5,172,958 and 5,154,491.
Normal operation of certain heavy duty vehicles such as waste pick-up vehicles and construction industry vehicles demand frequent parking brake applications in a short period of time as a result of numerous start-and-stop operations, which consume large volumes of compressed air. Such operations result in excessive brake system wear, undesirably reducing the useful life of air compressor, air dryer, and brake chamber components, and resulting in increased vehicle maintenance and repair costs.